Log in on the main Reallusion web page and click on "My Account" :
On your account page click on the icon beside your name to upload an image:
I can't remember the size restrictions, but perhaps that info is provided before uploading.
Gerry
System: Win 10 Pro (21H2), Asus X99-E WS, CPU i7-5930K -3,5 GHz, 32 GB DDR4 2666-16 RAM, NVidia GTX 1080 Ti GPU - 11 GB VRAM(Driver Studio-536.99), Samsung 850 Pro 512 GB SSD, 6 TB HD storage.